There is considerable current interest in the production of liquid fuels and chemical precursors from bio-derived waste materials, or polymer-containing feedstock.
Lignocellulosic biomass is of particular interest as a feedstock for production of renewable liquid biofuels and other commercially valuable compounds. It is a major structural component of woody and non-woody plants and consists of cellulose, hemicellulose and lignin. The aromatic carbohydrate polymers found in lignocellulosic biomass (primarily lignin) are of interest for production of high value platform chemicals, including monoaromatic compounds such as benzene, toluene, xylene, caprolactum, phenol, and their derivatives (e.g., guaiacol and catechol), which can be used for making a variety of chemicals and materials. Platform chemicals are important precursors for solvents, fuels, polymers, pharmaceutical, perfumes and foods.
Conversion of lignocellulosic biomass or a bio-derived feedstocks by pyrolysis involves many reaction steps leading to a liquid product that contains multiple components as well as significant water vapor, carbon oxides, and coke. The conversion process may be uncatalyzed, but catalysis improves the quality of the liquid product by removing oxygen in the liquid product, increasing the H:C ratio, and increasing the overall yield. Current methods for conversion of solid biomass to liquid components such as fuel involve multiple steps and long processing times, which greatly increases the cost of biomass processing. One process that has emerged as a viable technology to achieve such goals is fast pyrolysis. Fast pyrolysis converts many bio-derived materials to liquid hydrocarbons through a reductive conversion at elevated temperatures in a short amount of time.
It is envisioned that small conversion plants can be located nearby to large sources of biomass and convert the material to a liquid form which can be easily transported using existing infrastructure to refineries and chemical plants to be (co)processed in conventional hydrocarbon processing equipment. In order to realize this vision, the liquid products produced must possess properties which will allow for processing similar to fossil hydrocarbons and the value of the derived liquids and products must be sufficient to offset the added costs of the biomass processing step. For these reasons it is recognized that catalysts are needed in order to tune the properties and yields of the products. The catalyzed process is often referred to as catalytic fast pyrolysis (CFP).
CFP employs rapid heating of biomass in a non-oxidizing atmosphere to temperatures in the range of 400° C. to 600° C. in the presence of zeolite catalysts, and converts the biomass in a single step to gasoline-compatible aromatics. Although CFP requires shorter residence times and uses inexpensive catalysts, in general, the conversion of lignin and other biomass components to liquid hydrocarbons via CFP suffers from high coke yields and an acidic liquid product that has a high fraction of oxygen remaining. Furthermore, CFP produces large quantities of CO and CO2 as well as steam. The cause of all of these observations can be traced back to the oxygen content of the feed and the type of reactions that occur over conventional depolymerization catalysts. The cracking of carbohydrates, unlike hydrocarbons, results in the formation of highly reactive oxygenates. These oxygenates tend to condense with other oxygen containing moieties or with olefins to form coke. Any remaining oxygenates contribute to the acidity of the final product and the presence of oxygen in the reactor results in formation of CO, CO2, and steam. Thus, a catalyst for lignin CFP must be designed with these additional reactions taken into consideration. Typically, processing of biomass can also be done in a two-step process, wherein fast pyrolysis at 500° C.-700° C. is followed by catalyzed pyrolysis at about 400° C. The two-step process increases the yield of liquid, but is economically unfeasible. Further, it is desirable to use minimal or no external additives such as gases or liquids, other than the starting materials to reduce the operation and material cost in CPF processes.
Multi-step CFPs and/or CFPs that utilize additives are well known in the industry. For example, U.S. Patent Publication No. 2013/0030228 to Chen teaches a method to produce an aromatic hydrocarbon-containing effluent comprises the step of rapidly heating a biomass-based feedstock in the presence of a catalyst, hydrogen, and an organic solvent to form the aromatic hydrocarbon-containing effluent.
U.S. Patent Publication No. 2009/0227823 to Huber teaches compositions and methods for fluid hydrocarbon product via catalytic pyrolysis, which involves the use of a composition comprising a mixture of a solid hydrocarbonaceous material and a heterogeneous pyrolytic catalyst component.
U.S. Patent Publication No. 2013/0060070 to Huber teaches a method for producing one or more fluid hydrocarbon products from a solid hydrocarbonaceous material comprising:feeding solid hydrocarbonaceous material and hydrogen or a source of hydrogen to a reactor, then pyrolyzing the solid hydrocarbonaceous material, and catalytically reacting pyrolysis products and hydrogen to produce the one or more fluid hydrocarbon products.
U.S. Pat. No. 8,487,142 to Sarkar teaches a process for producing small molecular weight organic compounds from carbonaceous material, comprising a step of contacting the carbonaceous material with carbon monoxide (CO) and steam in the presence of a shift catalyst at a predetermined temperature and pressure.
U.S. Pat. No. 8,404,908 to Chen teaches a process includes reacting lignin with a hydrogenation catalyst under a hydrogen atmosphere to convert acidic oxygenate compounds to less acidic oxygenates or hydrocarbons. The oxygenate compounds are reacted in a dehydrogenation and a deoxygenation process to remove the oxygen, and to convert the cyclic hydrocarbons back to aromatic compounds.
The above-mentioned prior art teaches multi-steps or multi-stage processes, or the addition of external additives such as solvents and/or gases to initiate the depolymerization process of carbonaceous materials. Thus, there is a need for a single stage, one-pot process using a catalyst composition with minimal or no additives to produce liquid depolymerization products from polymers, such as production of monoaromatic compounds from lignin and lignocellulosic feedstock, with improved yields, reduced production of coke, and management of carbon monoxide. There is also a need for catalyst compositions that provide more economically viable processes by incorporating multiple catalytic functionalities in a single composition, thereby reducing the number of process steps required.